The invention refers to a method and an apparatus for measuring the volume of flowing liquids under avoidance of measuring errors by undesired high gaseous contents.
Method and apparatus are in particular suited for the use in tank trucks, e.g. for bunker oil or combustion oil or Diesel oil. During the delivery of liquid air may be trapped, above all by a change from one chamber of the tank truck to another chamber or during the complete evacuation of the chamber. An introduction of air into the liquid can also be caused by leakages of the conduit system. Further, air may be introduced during delivery by gravity owing to a subpressure in the conduit system. Gaseous contents, however, are falsifying the measurement of the volume of liquid delivered. Bureaus of standards, therefore, require that the gaseous contents of liquids are not to exceed desirable values.
To this purpose conventional measuring systems are provided with degassing means which include a collection container or vessel for air through which the liquid flows. Such degassing means have a level sensor which detects the collection of a predetermined volume of gas in order to stop the flow of liquid and to vent the container. By this it is secured that gauging means positioned downstream are not filled up with gases to an undesired amount so that undesired errors occur with measuring the volume of flowing liquids.
Furthermore, measuring systems are known working with electronic sensors which are suited to detect air bubbles in the flowing liquid and have an adjustable sensitivity. If a predetermined level of the air content is exceeded, the flow of liquid is stopped and the conduit is vented in order to avoid an undesired measuring value caused by an air content.
All known systems have the disadvantage that with a high technical inventory (means preventing the measuring of gas contents or bubble sensor with expensive degassing means) only signals are generated for two modes of this system. In one mode the delivering system delivers liquid under full power, and in the other mode the dispensing of liquid is completely interrupted and a venting process switched on. In case of liquid dispense under standard or gauge conditions this results in nervous switching phenomena between these modes. As a result, the delivery of liquid may be considerably delayed. Furthermore, the known measuring means consume a considerable space which has to be considered by the manufacturers of trucks. This above all is valid for apparatuses which prevent the measuring of gaseous liquids which normally are compact aggregates.
An object of the invention is to provide a method and an apparatus for measuring the volume of flowing liquids which require a reduced technical inventory, has a larger capacity and a reduced need of space.